Today NASA announced that it has successfully completed two more steps to align the mirrors of the Webb Telescope. The resulting performance demonstrates that Webb will meet or exceed his design goals. “So far we find that the performance is just as good [as] or better than our most optimistic projections,” said Lee Feinberg, optical telescope element manager at Webb.
The announcement was accompanied by a spectacular image showing sharp focus on the target star and containing many galaxies in focus in the background.
Get in line
The main mirror of the Webb telescope consists of an array of 18 individual segments that, once properly aligned, act as a single large mirror. The first steps in mirror alignment were to identify the images from each segment and merge those images into a single point. This work was completed in February. At this point, all the light was collected in one place, but it didn’t necessarily take the same path from each segment, meaning the segments weren’t acting as a single mirror.
Marshall Perrin, the element manager of Webb’s optical telescope, said the individual segments were microns from being properly aligned. The final alignment would bring the segments to nanometer-level precision — “a few hundred atomic diameters is the level of precision we need here,” Perrin said.
And apparently we have. “We have now achieved what is known as the diffraction-limited alignment of the telescope,” Perrin said. “The images are focused as finely as the laws of physics allow. This is as sharp an image as one can get from such a large telescope.”
“At no point in this process did we have any technical problems with the telescope – the major ones [surprise] is how closely it matched the models and predictions from Earth,” Perrin said. “Honestly, the team got dizzy at times looking at this data.”
There’s more to come
At this point, the mirror is aligned with the telescope’s main instrument, the near-infrared camera. However, the telescope has four additional instruments, and the next steps will be to align with each of the remaining instruments so that the mirrors are positioned to work well with all the hardware. In addition to NASA’s ability to tweak the positioning, shape and curvature of the segments, the secondary mirror and instruments themselves can be translated to ensure alignment.
Once this process is complete, final fine-tuning can be done, but after that there is nothing left but the ongoing calibration required to keep everything in sync. According to NASA, the alignment process should be completed by early May at the latest.
From there the science can begin – Jane Rigby of Webb Operations said a full year of scientific observations is already planned. Anyone associated with Webb will concede that some high-priority scientific targets have been chosen that are expected to produce aesthetically beautiful images, but no one has yet said what those are.
Right now everyone is concentrating on the galaxies that have come into view behind the star used for alignment. And the researchers are very relieved that the process went well. As Rigby put it, “There are days on this project where we would have walked home if things hadn’t worked out.” Instead, the whole process went smoothly.
Tom Zurbuchen, the administrator of NASA’s Science Mission Directorate, said: “Any worries I had are all behind us now.”
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